The study of petroleum analysis and its products would be incomplete without considering the incompatibility phenomenon in the crudes mixtures that causes changes in the original properties therein; i.e. during and after the crudes mixing, secondary products such as sludge, semisolids or solid particles increasing its viscosity and density, can be formed.
In short, the term incompatibility refers to the formation of a precipitate or sediment, or the separation of phases when the liquids are mixed.
Normally, the incompatibility processes in the crudes mixing increase petroleum or petroleum products viscosity, and it causes changes of viscosity in certain fuels even at low temperatures.
Some studies prove that the mixing of different crudes can lead to a flocculation/precipitation of asphaltenes. This phenomenon, known as crudes incompatibility causes more problems in the transportation and refinement, especially when the economical situation is forcing the refineries to carry out low cost crudes mixing to increase refining margins.
In spite of various studies carried out in the last decades, there are still important questions for chemical and physical knowledge of the incompatibility phenomenon. It is well known that this problem has not yet resulted into a standard method intended for the determination and quantification of incompatibility of crudes mixtures. Hence, several criteria for determining the crudes incompatibility are described in the literature.
On the other hand, the measurement of excess volumes started in 1983 by Dr. J. C. Cobos, ex-Laboratoire de Thermodynamique et Cinétique Chimique, now Laboratoire de Thermodynamique et Genie Chimique de L'Université Blaise Pascal (Clemront-Ferrant, France), using mechanical oscillation densitometer developed by Picker, Tremblay and Jolicoeur. At the beginning, there were two Picker models; in the first model the mechanical part was separated from the electronic part, presenting two modules, whereas in the second model both parts were included in only one module.
In 1986, the Thermodynamics group then called Thermology Department, now Thermodynamics Department and Applied Physics, acquired a densitometer based on the model of Stabinger, Leopold and Kraky. The vibrating element in this densitometer is a U shaped borosilicate tube that had a coil with heat exchanger function and that allow to work dynamically. Furthermore, a unit receiving oscillating signal was added to the densitometer, signal emitted by the densitometer output; afterwards, this second unit was substituted by a frequency meter.
J. F. Rodriguez made the data acquisition software and subsequently those of A. Cerna. F. J. Carmona and F. J. Arroyo followed. These last two added a temperature sensor to record temperature at which the liquid contained in the U shaped tube is contained, but as it was constantly breaking, it was necessary to substitute the cell containing it by the another one without coil and that allowed to carry out measurements at pressures up to 5 MPa.
The density of a homogenous substance is a physical property that characterizes it and is defined as the ratio between the substance mass and volume concerned. This property depends of the temperature that is why by measuring the density of a substance, the temperature at which measuring is carried out, must be considered.
In the case of non-homogenous substances, what is obtained is the mean density of the division of the mass and volume.
The incompatibility phenomenon of the petroleum-derived products is invariably associated with the chemical composition and physical relation of the components. In most cases, a certain component added to one of the fuels reacts with another component in the fuel with the one that is mixed. This chemical reaction results in the formation of a new product that, when is soluble, affects the mixing properties and when it is insoluble, is deposited as a semisolid or solid matter. Based on the above, different studies were carried out to determine, qualify, inhibit or prevent the formation of asphaltenes during manufacture, transportation and petroleum refining.
U.S. Pat. No. 7,029,570, dated Apr. 18, 2006, refers to a process for determining the incompatibility in crudes mixtures through the change in the dispersion length density of neutrons in the surface of asphaltene aggregates.
Carrier et al. in “Acoustic method for measuring asphaltene flocculation in crude oils”, Journal of Petroleum Science and Engineering 27 (2000), pp. 111-117, evaluated the presence of asphaltenes in crudes and developed an experimental device, based on an acoustic technique, for testing. In opaque systems, as the oil, the optical methods cannot be used to carry out its characterization that is why the transition of phases can be directly carried out, identifying breaking, discontinuity or the change of slopes of certain physical characteristics that accompany the change of phases, when temperature, pressure or composition of the system are altered.
Ekulu et al. in “Scanning Aggregation Phenomena in Crude Oils with Density Measurements”, Journal of Dispersion Science and Technology Vol. 25, No. 3, pp. 321-331, 2004, demonstrated that the density measurements can be used to evaluate changes of aggregation that are produced in a crude under the influence of chemical and physical factors. Apparent volumes and reduced densities are used to obtain graphs that clearly indicate the different steps of the aggregation phenomenon; the characteristic points of the graphs correspond to the well known phenomena that are produced in the crude, such as the flocculation incipient point of asphaltenes is called Critical Micellar Concentration (CMC). Also system density measurements were used (crude−toluene−n-heptane) for the determination of the flocculation incipient point of various crudes. This method was verified with flocculation data obtained with already established methods.
Tharanivasan et al. in “Measurement and Modeling of Asphaltene Precipitation from Crude Oil Blends”, Energy & Fuels 2009, 23, 3971-3980, developed a model using the regular solution theory to predict the appearance and quantity of precipitated asphaltenes of crude mixtures with pure n-alkanes or a toluene and n-heptane mixture. The tests were carried out with nine different crudes, a gasoil and its mixtures. The crudes and the mixtures were characterized in terms of SARA (saturated, aromatic, resins and asphaltenes) analysis fractions.
The references described in the state of the art, known by the applicant, were overcome through the present invention, since up to now there is not any reliable technique agreed to determine the incompatibility of heavy metals with light crudes.
An object of the present invention is to provide a reliable technique to determine incompatibility of heavy crudes with light crudes so as to be able to determine the proportions of light and heavy crudes suitable for mixing. Another object of the invention is to measure mixture densities of heavy crudes with light crudes at different temperature and pressure conditions.
Another object of the present invention is to measure the density of crudes mixtures with light crudes through a system or vibrating tube densitometry that provides quick and reliable results with uncertainty in the density measurement of 1 kg/m3, using 25 mL of sample.
The above and other objects of the present invention are provided as follows: